Paper: Human-Induced Changes in the Hydrology of the Western United States

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“Our results are not good news for those living in the western United States.”
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Science/www.sciencexpress.org / 31 January 2008 /

Human-Induced Changes in the Hydrology of the Western United States

Tim P. Barnett,1* David W. Pierce,1 Hugo G. Hidalgo,1 Celine
Bonfils,2 Benjamin D. Santer,2 Tapash Das,1 Govindasamy Bala,2 Andrew
W. Wood,3 Toru Nozawa,4 Arthur A. Mirin,2 Daniel R. Cayan,1 Michael
D. Dettinger1

1 -Scripps Institution of Oceanography, University of California, San
Diego, La Jolla, CA 92093, USA.
2 -Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
3 -Land Surface Hydrology Research Group, Civil and Environmental
Engineering, University of Washington, Seattle, WA 98195, USA.
4 -National Institute for Environmental Studies, 16-2, Onogawa,
Tsukuba, Ibaraki 305-8506, Japan.

*To whom correspondence should be addressed. E-mail: tbarnett-ul@ucsd.edu

ABSTRACT: Observations have shown the hydrological cycle of the
western U.S. changed significantly over the last half of the
twentieth century. Here we present a regional, multivariable
climate-change detection and attribution study, using a
high-resolution hydrologic model forced by global climate models,
focusing on the changes that have already affected this primarily
arid region with a large and growing population. The results show up
to 60% of the climate related trends of river flow, winter air
temperature and snow pack between 1950-1999 are human-induced. These
results are robust to perturbation of study variates and methods.
They portend, in conjunction with previous work, a coming crisis in
water supply for the western United States.

CONCLUSIONS:
Our results are not good news for those living in the western United
States. The scenario for how western hydrology will continue to
change has already been published using one of the models employed
here [PCM (2)] as well as in other recent studies of western US
hydrology [e.g., (15)]. It foretells of water shortages, lack of
storage capability to meet seasonally changing river flow, transfers
of water from agriculture to urban uses and other critical impacts.
Since PCM performs so well in replicating the complex signals of the
last half of the 20th century, we have every reason to believe its
projections and to act on them in the immediate future.

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